The present invention relates exclusively to the domain of mail processing and more particularly to a system for controlling the level of ink in a franking machine of the ink jet type.
In the specific domain of mail processing, the postal indicia is known to be a monetary value and the Postal Administrations see to it that the quality of print is sufficient to avoid any fraud on the amount of franking. Similarly, for the company using the franking machine, a mailpiece which has been returned due to defective indicia means a loss of the corresponding amount of franking, as this piece had been previously metered and can in no case be cancelled a posteriori.
Manufacturers of franking machines have thus sought a means for knowing with precision the ink consumed in such a machine in order to avoid launching prints of insufficient quality.
European Patent Application No. 0 881 079 proposes metering the drops of ink every time that a postal indicia is printed and, when the number thus obtained is higher than a previously set threshold corresponding to a minimum threshold of the ink reservoir of the franking machine, any subsequent printing is prohibited.
However, this system for controlling the level of ink in a franking machine lacks accuracy as, on the one hand, it essentially employs an average volume of ink corresponding to a typical postal indicia and, on the other hand, it does not take into account the fact that the volume of one drop of ink varies very substantially with the temperature attained at the level of the projection nozzles (of the order of 10 to 50%). As a result, this system might indicate the minimum level of ink attained, while the ink reservoir of the franking machine is still partially filled. Ink reservoirs which can still be used are therefore unnecessarily wasted.
U.S. Pat. No. 6,024,429 also proposes directly weighing the ink remaining in the reservoir, printing being prohibited if the weight obtained proves less than a predetermined value. Unfortunately, this solution, albeit simple, involves the user stopping the machine and removing the ink reservoir before weighing it and subsequently reassembling it if the limiting threshold is not yet attained.
It is an object of the present invention to overcome the drawbacks set forth hereinbefore, by proposing a system for controlling the level of ink in a franking machine which allows an automatic and sufficiently precise estimation of the volume remaining in its ink reservoir. A further object of the invention is to avoid dismantling the ink reservoir other than when it is to be discarded once it has been recognized as empty.
These objects are attained by a franking machine comprising:
a disposable head provided with an ink reservoir having a nominal volume of ink and memory means,
a base provided with means for controlling said head in order to:
activate this head in response to determined parameters of identification extracted from said memory means and recognized as valid by said base,
send franking data representative of postal indicia to be printed comprising static data and dynamic data,
calculate the number of droplets to be projected in order to print the dynamic data and add this number to that corresponding to the printing of the static data, previously memorized in said memory means, in order to obtain a total number of droplets to be projected for printing said postal indicia,
determine the volume of ink consumed corresponding to this total number of droplets to be projected and memorize this volume of consumed ink in said memory means, and
calculate the volume of ink remaining in said ink reservoir by subtracting said volume of ink consumed from said nominal volume of ink.
With this particular structure, the ink consumed may thus be calculated precisely without requiring any dismantling of the head and without unnecessary loss of ink due to an average estimation of consumption.
The disposable head further comprises a temperature sensor and the total number of droplets to be projected for printing said postal indicia is corrected as a function of the measured temperature of projection of the ink.
The memory means comprise a memory of EEPROM type.
The control means preferably further comprise means for furnishing the user with warning signals when predetermined threshold memorized in said memory means are exceeded. These predetermined thresholds comprise a first threshold corresponding to a xe2x80x9cfullxe2x80x9d ink reservoir with 100% of the nominal volume of ink, a second threshold corresponding to an ink reservoir xe2x80x9capproaching end of lifexe2x80x9d with 20% of the nominal volume of ink, a third threshold corresponding to an ink reservoir xe2x80x9cto be changed immediatelyxe2x80x9d with only 5% of the nominal volume of ink, and fourth threshold corresponding to an xe2x80x9cemptyxe2x80x9d ink reservoir with 0% of the nominal volume of ink.
The control means advantageously prohibit any fresh print when said third threshold at 5% is exceeded unless the user nonetheless continues printing.
The present invention also relates to the corresponding method for printing postal indicia in a franking machine comprising a base and a disposable head provided with ink jet printing means, characterized in that it comprises the following steps of:
activating said disposable head in response to determined parameters of identification extracted from memory means of this head and recognized as valid by said base,
sending towards said disposable head from said base franking data representative of postal indicia to be printed, comprising static data and dynamic data,
calculating in said base the number of droplets to be projected in order to print the dynamic data and add this number to that corresponding to the printing of the static data, previously memorized in said memory means, to obtain a total number of droplets to be projected for printing said postal indicia,
determining the volume of ink consumed corresponding to that total number of droplets to be projected and memorizing this volume of consumed ink in said memory means, and
calculating the remaining volume of ink in said ink reservoir by subtracting said volume of consumed ink from said nominal volume of ink.
According to an advantageous embodiment, the step of calculating the total number of droplets to be projected comprises a step of correction of this number as a function of the temperature of projection of the ink measured by means of a temperature sensor. Similarly, this step of calculating the total number of droplets to be projected comprises a step of correction of this number as a function of the operations of maintenance of the head.